The existing art discloses test sticks for determining total chlorine content, in particular total chlorine quantities in the range from 0.1 to 3 ppm in water, in which an indicator carrier in the form of an indicator paper, made of filter paper, is mounted on a stick and impregnated with an indicator solution. Present in the indicator carrier is a color indicator which, expressly avoiding potassium iodide, is made up solely of Michler's thioketone, and which is combined with an ionic, fluorinated surface-active agent (cf. EP 1 259 798 B1, in particular Claim 1 and paragraph [0025]). The pH of the color indicator is adjusted to 3 to 8, by preference 5, by the addition of acid or basic substances. Stabilizers can additionally be added to the indicator solution.
With the aid of the test stick, the concentration of total chlorine can be ascertained semiquantitatively as follows: starting from a 0 ppm total chlorine content, the initially yellow color changes, with higher total chlorine content, through dark green at 0.5 ppm to blue at 3 ppm. The color that is established in each case can then be compared with a color comparison chart, and the respective total chlorine content can be identified based on the concentration values associated thereon with the colors.
Also known are test sticks for ascertaining free chlorine content in aqueous solutions (see Hütter, Wasser and Wasseruntersuchung [Water and water investigation], 5th ed., 1992, page 149 for a definition of free, bound, and total chlorine). In these test sticks certain azines, in particular syringaldazines and vanillin azines, are used as color indicators, their pH being adjusted by means of a buffer to a value of 3.5 to 8.5. These test sticks are not suitable for determining total chlorine content.